If an officer suspects a person in Virginia is drunk driving, the officer may perform a field sobriety test before performing a breath test. There are three standard field sobriety tests that may be performed at a DUI stop. They include the horizontal gaze nystagmus test, the walk and turn test and the one-leg stand test.
The horizontal gaze nystagmus test is intended to measure intoxication based on the involuntary movements of the motorist's eyes. These movements may be exaggerated if a person is drunk. Officers performing this test will note whether the motorist can smoothly follow a moving object, whether the motorist's eyes involuntarily move within 45 degrees of their center and the involuntary movement of a motorist's eyes when they are at maximum deviation.
The walk and turn test is intended to measure intoxication based on a motorist's ability to do two or more tasks at once. The motorist will usually be asked to walk in a straight line by taking nine heel-to-toe steps, and then turn around using a single foot and head back the same way.
The one-leg stand test is meant to measure intoxication based on a motorist's ability to keep balance. The motorist will be asked to raise one foot about six inches high, standing on one foot for 30 seconds. The officer will note whether motorists sway, use their arms to keep balance, put their foot down or hop around.
While field sobriety tests are meant to provide officers with the information they need to determine if a motorist is intoxicated, the fact of the matter remains that they still must be performed and interpreted by a human being, and humans can make mistakes. For example, a person may call into question whether the test was properly performed or whether the officer correctly interpreted the results of the test. So, field sobriety tests -- even standardized ones -- may not be infallible. Those who were arrested for DUI based on the results of a field sobriety test may want to determine whether the test was properly performed and analyzed as they prepare their criminal defense strategy.